The present disclosure relates to image processing apparatuses, image processing methods, and electronic apparatuses and, in particular, to an image processing apparatus, an image processing method, and an electronic apparatus capable of effectively suppressing generation of false colors.
Up until now, solid state image sensors, for example, CCDs (Charge Coupled Devices), CMOS (Complementary Metal Oxide Semiconductor) image sensors, and the like, have been used in digital still cameras, digital video cameras, and other electronic apparatuses equipped with an imaging function. A solid state image sensor accumulates electric charges generated by photoelectric conversion in accordance with amount of incident light; and outputs electrical signals corresponding to the accumulated electric charges.
An upper limit exists on amount of electric charges to be accumulated for a photoelectric conversion element. If the photoelectric conversion element receives light above a certain level, the amount of the accumulated electric charges would reach its saturation level. As a result, so-called “blown out highlights” would occur in a subject region having brightness above a certain level, that is, intensity level of the subject region is set to the saturation level. In order to prevent an occurrence of such a phenomenon, for example, processing to control sensitivity to optimum value, by controlling an electric charge accumulation period for the photoelectric conversion element and, by adjusting an exposure time in response to the changes in the light outside, is performed.
For example, to a bright subject, the exposure time is shortened by high shutter speed, and thus the electric charge accumulation period for the photoelectric conversion element is shortened, thereby allowing the electrical signal to be output before the amount of the accumulated electric charges reaches its saturation level. Such processing enables output of an image with fully-reproduced gradations corresponding to the subject.
However, in imaging a subject including bright areas and dark areas, if the shutter is operated at a high speed, since the exposure time may not be enough for the darker areas, S/N (Signal/Noise) ratio would be decreased, and image quality is decreased. Thus, in order to fully reproduce the luminance level of the bright areas and the dark areas in an imaged picture of the subject including the bright areas and the dark areas, processing to realize high S/N ratio by making the exposure time longer for the pixels with relatively small amount of incident light on the image sensor; and to avoid saturation in the pixels with higher amount of incident light, may be needed.
In response to this, for example, with the use of HDR (High Dynamic Range) merge, which is made by varying the exposure time for every image and merging to one image a plurality of images that have been successively imaged, it would be possible to reproduce wide dynamic range that was not able to be reproduced by normal imaging.
Furthermore, instead of successively imaging the plurality of images as in the above processing, there has also been developed HDR merge processing to obtain one HDR image (high dynamic range image) by varying the exposure time for every pixel so that one image is imaged by different exposure times at a predetermined spatial period; and merging long-time exposure pixels and short-time exposure pixels within the image.
For example, an imaging apparatus which takes images in an SVE (Spatially Varying Exposure) mode; the exposure mode which varies the exposure time for each light-receiving element, in several patterns for every light-receiving element, has been disclosed in Japanese Patent Application Laid-Open No. 2002-118789.
In addition, according to processing disclosed in Japanese Patent Application Laid-Open Nos. 2013-66145 and 2012-257193, at the time of processing to merge pixels of different exposure times and different sensitivities from each other, a gain multiplication by a value determined from a set exposure time ratio, a previously-calculated sensitivity ratio, or the like, would be applied to a pixel signal having the lower signal amount. The resulting value and a pixel signal having the higher signal amount would be combined at a certain composition ratio.
Besides, as a method of making corrections to false color signals in the merged signals, a technique that makes the color of the subject region nearer to an achromatic color has been suggested in Japanese Patent Application Laid-Open No. 2011-87269.